Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth. Wind flow patterns are modified by the earth's terrain, bodies of water, and vegetative cover.
Next is the lower-middle class, which is primarily comprised of lower-level, white-collar workers. These workers typically have college educations, but lack the graduate degrees needed to advance to higher levels of employment. Income for these workers generally falls between $32,500 and $60,000. Upper-middle-class workers typically have post-graduate degrees and work at high-level, white-collar positions. Household income for these workers is often above $100,000. According to the Census bureau, upper-middle-class, or professional class workers, earn enough to be in the top one-third of American incomes.
Here's how much you have to earn to be considered middle class. The American middle class keeps shrinking. The share of American adults in middle-income households also decreased, from 55% in 2000 to 51% in 2014, Pew Research Center reports. At the same time, the share of adults in the upper-income tier increased from 17% to 20%. Although income is just one part of class, it's a crucial element and the one that's easy to measure and track. So just how much do you need to make to qualify as middle class these days? Pew, which defines middle class as adults whose annual household income is two-thirds to double the national median ($55,775 as of 2016), details the national middle-income range for various household sizes.